This invention relates in general to electrophotography and, more specifically, to a process for preparing an electrophotographic imaging member.
The formation and development of images on the imaging surfaces of electrophotographic imaging members by electrostatic means is well known. One of the most widely used processes being xerography described, for example, in U.S. Pat. No. 2,297,691. Numerous different types of photoreceptors can be used in the electrophotographic imaging process. Such electrophotographic imaging members may include inorganic materials, organic materials, and mixtures thereof. Electrophotographic imaging members may comprise contiguous layers in which one of the layers performs a charge generation function and the other layer forms a charge carrier transport function or may comprise a single layer which performs both the generation and transport functions.
It is customary in the art of electrophotography to form an electrostatic latent image on an electrophotographic imaging member comprising an electrically conductive backing such as, for example, a metallic or metal-coated base having an inorganic photoconductive insulating layer applied thereto in good charge blocking contact. Typical electrophotographic imaging members comprise, for example, an aluminum surface having a thin layer of vitreous selenium with an aluminum oxide and/or polymeric interlayer. Such elements are characterized by being capable of accepting and retaining a suitable uniform electrostatic charge in the dark and of quickly and selectively dissipating a substantial part of the charge when exposed to a light pattern.
As more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, stringent requirements have been placed on these complex, highly sophisticated systems including long operating life with minimum maintenance requirements. For example, the supporting substrate for electrophotographic imaging members in various configurations such as drums and belts must meet precise tolerance standards and adhere well to photoconductive insulating layers applied thereto. The aluminum drums utilized as supporting substrate material for rigid drum-shaped supporting substrates are relatively expensive; often require replacement due to wear prior to the need to replace the photoconductive insulating layer; are susceptible to wobble due to counterbores that are easily damaged; exhibit narrow coating process latitude; often exhibit poor alloy adhesion characteristics; and often exhibit variable electrical parameters due to the aluminum oxide layer. Moreover, latching and polishing of aluminum drums are necessary prerequisites to achieving a uniform surface for subsequently applied photoconductive insulating layer or layers. Moreover, aluminum drums must necessarily be thick in order to achieve adequate rigidity to meet the stringent tolerence requirements of precision machines. Heavy drums require more powerful drive systems and rugged clutches to overcome high inertia characteristics.
It has been discovered that lightweight electroformed nickel drums and belts may be utilized to address the poor tolerence and inertia characteristics of aluminum substrates. However, coatings of photoconductive insulating layers such as selenium or selenium alloys on nickel surfaces and particularly electroformed nickel substrates, often flake off from the substrate within about a month after application of the coatings. Although synthetic polymer coatings may help minimize flaking, additional coating and drying process steps and as well as coplex equipment are necessary.
The adhesion of photoconductive insulating layers to metal substrates such as nickel may be improved by special chemical treatments. For example, a process is described in U.S. Pat. No. 3,907,650 to Pinsler and in U.S. Pat. No. 3,914,126 to Pinsler in which a nickel substrate is subjected to an acid etching bath followed by an anodizing treatment in an electrolytic bath to obtain at least two intermediate metal oxide layers such as nickel oxide layers. This technique is relatively complex and the resulting surface tends to be somewhat rough. In addition, the Pinsler process requires multiple steps, costly equipment, produces fumes and presents a waste disposal problem.
In U.S. Pat. No. 4,019,902 to L. Leder et al, a nickel substrate is initially bombarded as a cathode, with positive ions of an inert gas of low ionization potential under glow discharge in the presence of oxygen and the resulting oxide-coated substrate is exposed to a vapor cloud of photoconductive material consisting of charged and uncharged material in an electrical field utilizing the metal substrate as a cathode and a donor of the vapor cloud of photoconductive material or container thereof as a anode. After completion of glow discharge treatment sufficient to ion clean the surface, formation of an oxide barrier of about 10-200 Angstroms thickness and heating of the substrate to a temperature of about 55.degree. C.-80.degree. C. (about 5-20 minutes and preferably 8-10 minutes), the heated oxidized substrate (cathode) is simultaneously exposed to a cloud of charged and uncharged photoconductive particles evolved from a heated photoconductor source in and adjacent to a region of glow discharge. This complex process improves the adhesion of photoconductive insulating layers to nickel substrates but the overall photoreceptor life is only about one year due to the eventual formation of NiSe and resulting adhesion loss. Moreover, costly and sophisticated equipment is required to carry out the process.
Thus, there is a continuing need for processes for preparing electrophotographing imaging members having nickel substrates that exhibit improved adhesion to photoconductive insulating layers.